You won't have any difficulties with Velvia if you expose it for its intended illumination, that being diffuse, rather than point (e.g. bright sun). Having said that, Velvia 100 is an extreme palette (commonly referred to as an "ultra-high saturation palette") with touchy whites and hyper-elevated reds and blue, and blows highlights and block shadows far less gracefully than the stablemate Velvia 50 (commonly rated at EI40) or 100F (rated as-is).
Either/both of the above will be quite noticeable in projection, but unless you are printing, it is no big deal. Things get very serious indeed when it comes time to print Velvia which exposure has been compromised in some place.
It is recommended that you bracket several of your shots either side of the nominal ISO and decide from there. Clip tests at the processing stage may also be useful in coming to a working conclusion as to which ISO/index is best suited to the photography you do, but it won't be a "one shoe fits all" outfit, hence the other Velvia emulsions are worth looking at too.